Currently, object-oriented program design dominates all methods of program design. In the field of object-oriented program design, an object refers to an entity that has a state and a set of operations defined on the state. The state is represented as a set of object attributes. The set of operations associated with the object provide other objects (clients) which request services when requiring some computation with the requested services. Object classes are used to create objects. An object class definition serves as a template for objects which includes declarations of all attributes and services associated with an object of the class. Object persistency means that an object is stored into storage such that the object will not be lost even when power is down. In a JVM (Java Virtual Machine), an object is generally stored into a RAM heap which is volatile, that is, the object data stored in the RAM heap will be lost when the RAM heap is powered-down. Java is a trademark or registered trademark of Oracle and/or its affiliates in the United States, other countries, or both.
An application usually needs to persist some, but not all, objects. Such persistency needs to go through a separate persistency layer. For example, a database usually includes a data portion and an interface such as an API (Application Programming Interface) which can be considered as the persistency layer. During exterior programming to access the database, in addition to statements for normal operations, the specific statements for persisting object data via the API are needed to be written. If such programming work is to be done for each of different databases, the workload is extremely enormous, and it is time consuming, exacting and error-prone. Thus, current object persistency methods and systems need separate persistency layers, heavy weight programming models, and high development and runtime costs.
On the other hand, there has appeared PCM (Phase Change Memory). The PCM has characters in that it is data-nonvolatile and can be addressed according to bytes, which results in the storing speed of the PCM being very fast, and the PCM can be used as working memory (RAM) of CPU, and data can be stored persistently in the meantime.